Dual Mode Power Transfer Switches

The field of the disclosure relates to power transfer switches, and in particular, to power transfer switches that implement different transfer modes depending on various criteria or trigger conditions.

A transfer switch is a device that is designed to transfer a load from a preferred power source to an alternate power source when the power quality of the preferred power source is deemed unacceptable for the load. An automatic transfer switch (ATS) typically uses contactors to transfer a load, where the contactors are electrically controlled mechanical switches that open one set of power contacts while closing a second set of power contacts. Due to the mechanical nature of the contactors used in in an ATS, an ATS typically requires multiple line cycles to transfer the load from the preferred source to the secondary power source (e.g., fifty to one hundred milliseconds or more).

Static transfer switches (STS) utilize solid-state power stages such as thyristors, silicon carbide (SiC) metal-oxide semiconductor field-effect transistors (MOSFETs), or other types of solid-state devices as the main switching device. Solid-state power stages are capable of transferring a load from the preferred power source to the alternate power source in less than one half line cycle (e.g., less than about eight milliseconds).

Although an STS achieves a much faster transfer time than an ATS, failures in a power stage of the STS can prevent load transfers from the primary power source to the alternate power source under certain conditions. The result is that it may not be possible to transfer the load from the primary power source to the alternate power source if the primary power source fails or is deemed unacceptable for the load, which is undesirable.

Thus, it is desirable to improve the operation and performance of STSs for load transfers when certain conditions arise.

In one aspect, a transfer switch configured to operate in different transfer modes is provided. The transfer switch includes first and second inputs, first and second contactors, an output, first and second power stages, and a controller. The first and second inputs are configured to couple with first and second power sources, respectively. The first and second contactors are configured to selectively couple with the first and second inputs, respectively. The output is configured to couple with a load. The first and second power stages are configured to conduct electrical power when active, where the first power stage is configured to selectively couple the first contactor with the output, and where the second power stage is configured to selectively couple the second contactor with the output. The controller is communicatively coupled with the first and second power stages and the first and second contactors. The controller is configured to determine whether a trigger condition has occurred while the first power stage is active, and in response to determining that the trigger condition has occurred, the controller is further configured to open the first contactor and activate the second power stage to transfer the load from the first power source to the second power source.

In another aspect, a method operable by a controller of a transfer switch of operating the transfer switch in different transfer modes is provided. The transfer switch includes first and second inputs, first and second contactors, an output, and first and second power stages. The first and second inputs are coupled with first and second power sources, respectively. The first and second contactors selectively couple with the first and second inputs, respectively. The output is coupled with a load. The first and second power stages conduct electrical power when active, where the first power stage selectively couples the first contactor with the output, and where the second power stage selectively couples the second contactor with the output. The method includes determining whether a trigger condition has occurred while the first power stage is active, and in response to determining that the trigger condition has occurred, opening the first contactor and activating the second power stage to transfer the load from the first power source to the second power source.

In another aspect, a transfer switch configured to alternate between automatic transfer switch (ATS) mode and static transfer switch (STS) mode is provided. The transfer switch includes first and second inputs, first and second contactors, an output, first and second power stages, and a controller. The first and second inputs are configured to couple with first and second power sources, respectively. The first and second contactors are configured to selectively couple with the first and second inputs, respectively. The output is configured to couple with a load. The first and second power stages are configured to conduct electrical power when active, where the first power stage is configured to selectively couple the first contactor with the output, and where the second power stage is configured to selectively couple the second contactor with the output. The controller is communicatively coupled with the first and second power stages and the first and second contactors. The controller is configured to operate the transfer switch in the ATS mode using one of the first and second contactors and one of the first and second power stages to transfer the load between the first and second power sources, and to operate the transfer switch in the STS mode using the first and second power stages to transfer the load between the first and second power sources.

Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of this disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of this disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein.

In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings.

The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

As used herein, the terms “processor” and “computer,” and related terms, e.g., “processing device,” “computing device,” and “controller” are not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a microcontroller, a microcomputer, an analog computer, a programmable logic controller (PLC), an application specific integrated circuit (ASIC), and other programmable circuits, and these terms are used interchangeably herein. In the embodiments described herein, “memory” may include, but is not limited to, a computer-readable medium, such as a random-access memory (RAM), a computer-readable non-volatile medium, such as a flash memory. Alternatively, a floppy disk, a compact disc—read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a digital versatile disc (DVD) may also be used. Also, in the embodiments described herein, additional input channels may be, but are not limited to, computer peripherals associated with an operator interface such as a touchscreen, a mouse, and a keyboard. Alternatively, other computer peripherals may also be used that may include, for example, but not be limited to, a scanner. Furthermore, in the example embodiment, additional output channels may include, but not be limited to, an operator interface monitor or heads-up display. Some embodiments involve the use of one or more electronic or computing devices. Such devices typically include a processor, processing device, or controller, such as a general-purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a reduced instruction set computer (RISC) processor, an ASIC, a programmable logic controller (PLC), a field programmable gate array (FPGA), a digital signal processing (DSP) device, and/or any other circuit or processing device capable of executing the functions described herein. The methods described herein may be encoded as executable instructions embodied in a computer readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a processing device, cause the processing device to perform at least a portion of the methods described herein. The above examples are not intended to limit in any way the definition and/or meaning of the term processor and processing device.

As discussed previously, various conditions can arise in STS that may prevent the STS from transferring the load from a preferred power source to an alternate power source when the preferred power source is incapable of supplying electrical power to the load. For example, when power stages are used to transfer the load between power sources, a short in a power stage may prevent the power stage from being deactivated to allow the transfer. It is not possible maintain both power stages active at the same time, as this would result in short circuit path between the two power sources, which may not be synchronized in voltage and frequency. Therefore, a short circuit in one of the power stages may prevent the power transfer from occurring.

In the embodiments described herein, transfer switches are disclosed that utilize both contactors and power stages to operate the transfer switch in different modes. When the transfer switch operates in an STS mode, the transfer switch utilizes the power stages to quickly transfer the load (e.g., within one line cycle) between primary power sources (e.g., preferred power sources) and secondary power sources (e.g., alternate power sources) while the contactors are closed. When the transfer switch operates in an ATS mode, the transfer switch utilizes one of the contactors and one of the power stages to transfer the load between the primary and secondary power sources (e.g., typically within about 50 milliseconds (ms) to about one hundred ms). For example, if a power stage is shorted in the primary power source current path and cannot be disabled, a power transfer can still occur from the primary power source to the secondary power source by opening the contactor in the primary power source current path and activating the alternate power stage in the current path of the secondary power source. Although this ATS mode transfer may take longer than a normal STS mode transfer (e.g., longer than one line cycle), the load is still able to be transferred even though one of the power stages is shorted. The result is more reliable protection of the load from transient faults at the primary power source and/or the active power stage supplying power to the load.

depicts a simplified circuit diagram of a transfer switchin an exemplary embodiment. In this embodiment, transfer switchselectively supplies a loadwith electrical power from either a first power sourceor a second power sourcedepending on various criteria or trigger conditions. For example, transfer switchmay supply electrical power to loadprimarily from first power sourceunless the electrical power delivered by first power sourcefalls outside of a desired range of values (e.g., first power sourcehas a voltage, and/or frequency, and/or a harmonic distortion that varies from target values by a threshold amount). If, for example, first power sourceis incapable of supplying electrical power to load(e.g., first power sourcefails or is incapable of supplying electrical power to loadat a desired power quality), then transfer switchswitches loadfrom first power sourceto second power source. In this regard, first power sourcemay operate as a preferred power source for load, with second power sourceoperating as a backup or alternate power source for load.

Although only two power sources for loadare depicted in, transfer switchselectively couples loadto any number of power sources in other embodiments. Further, although transfer switchis depicted as switching single phase Alternating Current (AC) power in, transfer switchswitches 3-phase AC power in other embodiments. In 3-phase AC embodiments, first power sourceand second power sourceare 3-phase AC sources, and loadis a 3-phase AC load. In other embodiments, first power sourceand second power sourceare Direct Current (DC) sources, and loadis a DC load. In other embodiments, first power sourceand second power sourceare 3-phase AC sources, and transfer switchsupplies a plurality of single-phase AC loads (e.g., loadis a plurality of single-phase AC loads).

In this embodiment, first power sourceis electrically coupled to transfer switchat a first inputand second power sourceis electrically coupled to transfer switchat a second input. Transfer switchfurther includes a first contactor, a second contactor, a first power stage, a second power stage, a controller, and an output. Generally, first and second contactors,comprise any component, system, or device that provides galvanic isolation between their respective first and second inputs,and first and second power stages,(e.g., first and second contactors,may comprise an electro-mechanical device that provides galvanic isolation via an air gap when opened). First and second contactors,may be opened and closed via commands or signals provided by controller. Further, first and second contactors,may not be externally accessible at transfer switchby an operator in some embodiments, and further still, first and second contactors,may not provide overcurrent trip capabilities in some embodiments.

First and second power stages,may comprise SiC MOSFETS, thyristors, or other types of solid-state switches, which selectively couple first and second contactors,with output.

Controllercomprises any component, system, or device that performs the functionality described herein for controller. Outputin this embodiment is coupled to load.

In this embodiment, transfer switchis configured to operate in different transfer modes based on various detected trigger conditions. For example, transfer switchmay alternate between operating in an STS mode and operating in an ATS mode depending on whether controllerdetects various criteria, referred to as trigger conditions. During normal operation of transfer switch, controllermay operate transfer switchin STS mode, switching loadbetween first and second power sources,using first and second power stages,while first and second contactors,remain closed. When a trigger condition is detected by controller, controllermay operate transfer switchin ATS mode, switching load between first and second power sources,by opening one of first and second contactors,and activating one of first and second power stages,.

During normal operation, first power sourceis the preferred power source for loadand second power sourceis the backup or alternate power source for load. First and second contactors,are closed, first power stageis active (e.g., first power stageconducts current) and second power stageis inactive (e.g., second power stagedoes not conduct current).

If controllerdetermines that first power sourceis not capable of supplying electrical power to load(e.g., due to power loss at first power sourceor a power quality issue at first power source), then controlleroperates transfer switchin STS mode to quickly transfer load(e.g., within one line cycle) from first power sourceto second power sourceby activating second power stageand deactivating first power stage(e.g., using a load transfer process).

However, various trigger conditions may arise at transfer switchwhich may prompt controllerto switch transfer switchfrom STS mode to ATS mode and transfer loadfrom first power sourceto second power sourceusing first and/or second contactors,. When these trigger conditions occur, controlleroperates transfer switchin ATS mode to transfer loadfrom first power sourceto second power sourceusing first contactorand second power stage. To do so, controlleropens first contactorand activates second power stage, which transfers loadfrom first power sourceto second power source. The result is that loadis transferred, albeit slower (e.g., within more than one line cycle) than when using STS mode, to second power source.

If controllerdetects that these trigger conditions are resolved, then controllermay operate transfer switchin STS mode to transfer loadfrom second power sourceto first power source. To do so, controllercloses first contactor, deactivates second power stage, and activates first power stageusing a load transfer process, which transfers loadfrom second power sourceto first power source.

One example of detecting a trigger condition includes determining, by controller, that the power quality of first power sourceis outside of a pre-defined range (e.g., a voltage, and/or a frequency, and/or harmonic distortion of first power sourceis outside of a pre-defined range). If controllerdetermines that the power quality of first power sourceis outside of a pre-defined range, then controllermay operate transfer switchin ATS mode as described above to transfer loadfrom first power sourceto second power sourceby opening first contactorand activating second power stage. This may be used, for example to prevent damage to first power stagefrom first power sourceby opening first contactor. Similar to discussed above, if controllerdetects that the power quality of first power sourcehas improved such that the power quality is now within the predefined range, then controllermay operate transfer switchin STS mode as described above to transfer loadfrom second power sourceto first power source by closing first contactor, deactivating second power stage, and activating first power stageusing a load transfer process, which transfers loadfrom second power sourceto first power source.

Another example of detecting a trigger condition includes determining, by controller, that first power stageis incapable of being deactivated. For example, first power stagemay be non-responsive, partially damaged, or electrically shorted in an active state of electrical conduction. If controllerdetermines that first power stage is incapable of being deactivated or electrically shorted, then controllermay operate transfer switchin ATS mode as described above to transfer loadfrom first power sourceto second power sourceby opening first contactorand activating second power stage. Similar to discussed above, if controllerdetects that the issues at first power stageare resolved (e.g., first power stageis now capable of being deactivated and/or is no longer electrically shorted), then controllermay operate transfer switchin STS mode as described above to transfer loadfrom second power sourceto first power source by closing first contactor, deactivating second power stage, and activating first power stageusing a load transfer process, which transfers loadfrom second power sourceto first power source.

Although first power sourcehas been describe as the primary power source and second power sourcehas been described as the secondary power source for load, the opposite is also possible with second power sourcenormally powering loadwith first power sourceas the backup or alternate power source. The result of this is that operations described above for the first and second power sources,, the first and second contactors,, and first and second power stages,are reversed.

depicts a block diagram of controllerin an exemplary embodiment. Controllerwill be described with respect to various discrete elements, which perform functions. These elements may be combined in different embodiments or segmented into different discrete elements in other embodiments. In this embodiment, controllercomprises at least one processor, at least one interface, at least one memory, a user interface, and at least one sensor. In some embodiments, memorystores programmable instructions that control the operation of processorin order to implement the functionality described herein for controller. In some embodiments, controllercomprises a different configuration of components, and therefore, the discussion of controlleris not limited to the specific configuration and arrangement depicted in.

Interfacemay comprise wired interfaces, wireless interfaces, and combinations thereof. Interfacemay be used by controllerto communicate with the various components of, such as first and second contactors,and first and second power stages,in order to control to control their operation and/or in order to determine their open/inactive and closed/active states. User interfacemay comprise keypads, display devices, trackball devices, mice, buttons, and the like, which enable an operator to interact with transfer switch. Sensorscomprise any voltage sensor, current sensor, frequency sensor, other types of sensors, and combinations thereof. Sensorsmay be used by controllerto determine the operating states (e.g., open/inactive or closed/active) of the various switching components of, such as first and second contactors,and first and second power stages,. Sensorsmay also be used to evaluate the operation and/or the power quality at first and second power sources,, measure various electrical parameters at first and second inputs,, output, determine the health of first and second power stages,, determine whether first and second power stages,are electrically shorted, determine whether first and second power stages,are no longer electrically shorted, etc.

depicts a flow chart of a methodoperable by a controller of a transfer switch of operating the transfer switch in different modes in an exemplary embodiment. Methodwill be discussed with respect to transfer switchof, although methodmay apply to other configurations of transfer switches, not shown.

Methodcomprises determining, by the controller, whether a trigger condition has occurred while the first power stage is active, and the first power source is powering the load. For example, processorof controllerdetermines whether a trigger condition has occurred while first power stageis active and first power sourceis powering load(see). To do so, processormay utilize sensorsand/or interfacesto determine whether the trigger condition has occurred. As discussed above, the trigger condition may include determining, by processor, that first power stageis incapable of being deactivated, determining, by processor, that first power stageis electrically shorted in an active state of electrical conduction, determining, by processor, that the power quality of first power sourceis outside of a pre-defined range (e.g., outside of a predefined voltage, and/or a pre-defined frequency, and/or a pre-defined harmonic distortion, etc.).

If the trigger condition has occurred, then methodfurther comprises openingthe first contactor and activatingthe second power stage to transfer the load from the first power source to the second power source. For example, processorof controlleropens first contactorand activates second power stage(see).

Methodfurther comprises determining, by the controller, whether the trigger condition has ended. For example, processorof controllerdetermines whether a trigger condition has ended utilizing sensorsand/or interfaces. As discussed above, determining that the trigger condition has ended may include determining, by processor, that first power stageis now capable of being deactivated, determining, by processor, that first power stageis no longer electrically shorted in an active state of electrical conduction, determining, by processor, that the power quality of first power sourceis within of a pre-defined range (e.g., within of a predefined voltage, and/or a pre-defined frequency, and/or a pre-defined harmonic distortion, etc.).

If the trigger condition has ended, then methodfurther comprises closingthe first contactor, activatingthe first power stage, and deactivatingthe second power stage to transfer the load from the second power source to the first power source. For example, processorof controllercloses first contactor, activates first power stage, and deactivates second power stage(see).

depicts another flow chart of another methodoperable by a controller of a transfer switch of operating the transfer switch in different modes in an exemplary embodiment. Methodwill be discussed with respect to transfer switchof, although methodmay apply to other configurations of transfer switches, not shown.

Methodcomprises determining, by the controller, whether a trigger condition has occurred while the second power stage is active and the second power source is powering the load. For example, processorof controllerdetermines whether a trigger condition has occurred while second power stageis active and second power sourceis powering load(see) utilizing sensorsand/or interfaces. As discussed above, the trigger condition may include determining, by processor, that second power stageis incapable of being deactivated, determining, by processor, that second power stageis electrically shorted in an active state of electrical conduction, determining, by processor, that the power quality of second power sourceis outside of a pre-defined range (e.g., outside of a predefined voltage, pre-defined frequency, and/or a pre-defined harmonic distortion, etc.).

If the trigger condition has occurred, then methodfurther comprises openingthe second contactor and activatingthe first power stage to transfer the load from the second power source to the first power source. For example, processorof controlleropens second contactorand activates first power stage(see).

Methodfurther comprises determining, by the controller, whether the trigger condition has ended. For example, processorof controllerdetermines whether a trigger condition has ended utilizing sensorsand/or interfaces. As discussed above, determining that the trigger condition has ended may include determining, by processor, that second power stageis now capable of being deactivated, determining, by processor, that second power stageis no longer electrically shorted in an active state of electrical conduction, determining, by processor, that the power quality of second power sourceis now within the pre-defined range (e.g., within the predefined voltage, and/or the pre-defined frequency, and/or the pre-defined harmonic distortion, etc.).

If the trigger condition has ended, then methodfurther comprises closingthe second contactor, activatingthe second power stage, and deactivatingthe first power stage to transfer the load from the first power source to the second power source. For example, processorof controllercloses second contactor, activates second power stage, and deactivates first power stage(see).

An example technical effect of the apparatus and method described herein includes one or more of: (a) minimizing disruptions to a load by alternating a transfer switch between STS and ATS mode depending on detected triggers; and (b) eliminating failure modes in a typical STS using contactors to transfer the load between power sources during transient faults at the power sources and/or the power stages of the transfer switch.

Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.

This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.